1. Field of the Invention
The present invention relates to a fitting for connecting pipes that carry fluid or gas, and more particularly, a fitting that can be connected to a pipe by using a fluid powered sizing apparatus.
2. Description of the Prior Art
Fittings for connecting the ends of pipes are old in the art. The earliest method of fitting two pipes together involved a simple member with an outside diameter that is larger than the pipe to be inserted, creating a snug fit between the two pipes as shown in U.S. Pat. No. 2,121,558. The telescopically inserted pipe could then be either glued are soldered to form a liquid or gas tight seal. The problem with this early design was the inconvenience of using either glue or solder. Further, these pipe fittings did not prove to be adequate for high pressures (above 500 psi).
The earlier pipe fittings were improved upon by creating a member with a complex inner surface that contacted the telescopically inserted pipe. This complex surface consists of such designs as curved grooves as in U.S. Pat. No. 5,080,406, or "teeth" and a lock-ring as in U.S. Pat. No. 4,482,174, or annular grooves as in U.S. Pat. No. 5,452,921. Each of these fittings are designed to operate by inserting a pipe within the complex inner surfaced member and swaging the outer surface of the member. The drawback to these designs is that the inner grooves and teeth create a deformation in the pipe that is inserted. This creates areas of high stress concentrated at specific points in the pipe. It is these high stress areas that are major factors in the incidence of failure in pipe fittings. Furthermore, in order for these fittings to work properly, they must be large and relatively heavy. These characteristics make the prior art fittings undesirable for smaller high pressure fittings.
Other pipe fitting devices can incorporate an "O" ring and adhesives to help form a tight seal as in U.S. Pat. No. 4,330,924. However, this device is also swaged in such a manner as to deform the pipe member that is within the outer fitting member. Also, this and other designs are not as versatile as desired due to the dual nature of the design--both the female (fitting) and male (pipe) portions of the device are designed to work together exclusively. This limits the use of the joint to pipes that are specifically tailored to fit the joint. Thus, while there have been improvements in pipe fittings from the earliest inventions, there is still a need for easier to use fittings. In particular, there is a need for improved fittings for commercial use where qualities such as weight, durability, and low cost are critical factors.